The present invention relates generally to trace gas detection and more specifically to cavity enhanced absorption spectroscopy systems and methods for measuring trace gases.
Traditionally, in standard applications of cavity enhanced absorption spectroscopy methods with resonant cavities, lasers with smooth frequency tuning behaviors are preferable. It is also important to have lasers with smooth frequency tuning behaviors for tunable diode laser absorption spectroscopy applications, e.g, TDLAS or Off Axis ICOS, where concentrations of absorbing gas species are measured by measuring absorption spectra of different species as function of wavelength and fitting them using spectral line-shape models. Unless a very precise wave-meter is used to measures the laser light frequency, any deviations in the laser tuning curves from ideal may cause errors in the reported concentration values.
In addition to that, if a DFB laser is used in a cavity enhanced laser based gas analyzer system as a light source, an electrical noise of the laser diode current causes an additional noise in the laser frequency. Moreover, any unwanted discontinuity in the laser current tuning, for example, due to the quantization noise of a finite resolution of a digital-to-analog converter, can be transferred to a discontinuity of the laser frequency.
Accordingly, there is a need for systems and methods for trace gas detection using lasers with improved performance coupled to resonance optical cavities.